package class06;

import java.util.Stack;

/**
 * @author zhangchaoliang
 * create 2022
 */
public class IsPalindromeList2 {
    public static class Node{
        public int value;
        public Node next;

        public Node(int data){
            this.value = data;
        }
    }

    public static boolean isPalindrome1(Node head){
        Stack<Node> stack = new Stack<>();
        Node cur = head;
        while (cur!=null){
            stack.push(cur);
            cur =cur.next;
        }
        while (head!=null){
            if (head.value!=stack.pop().value)
                return false;
        }
        return true;
    }

    public static boolean isPalindrome2(Node head){
        if (head==null||head.next==null)
            return true;
        Node cur = head;
        Node right = head.next;
        while (cur.next!=null&&cur.next.next!=null){
            right=right.next;
            cur =cur.next.next;
        }
        Stack<Node> stack = new Stack<>();
        while (right!=null){
            stack.push(right);
            right = right.next;
        }
        while (!stack.isEmpty()){
            if (head.value!=stack.pop().value)
                return false;
            head=head.next;
        }
        return true;
    }

    public static boolean isPalindrome3(Node head){
        if (head==null||head.next==null)
            return true;
        Node n1 = head;
        Node n2 = head;
        while (n2.next!=null&&n2.next.next!=null){
            n1 = n1.next;
            n2 = n2.next.next;
        }

        n2=n1.next;
        n1.next=null;
        Node n3 = null;
        while (n2!=null){
            n3 = n2.next;
            n2.next = n1;
            n1=n2;
            n2=n3;
        }
        n3=n1;
        n2=head;
        boolean res = true;
        while (n1!=null&&n2!=null){
            if (n1.value!=n2.value){
                res=false;
                break;
            }
            n1=n1.next;
            n2=n2.next;
        }
        n1=n3.next;
        n3.next=null;
        while (n1!=null){
            n2=n1.next;
            n1.next=n3;
            n3=n1;
            n1=n2;
        }
        return res;
    }
}
